Grassley sent a letter to FBI Director Christopher Wray on Wednesday asking if the bureau had given "defensive briefings" or otherwise alerted Trump officials about "potential connections between campaign officials and the Russian government."

"If the FBI did provide a defensive briefing or similar warning to the campaign, then that would raise important questions about how the Trump campaign responded," wrote Grassley, the chairman of the Judiciary Committee.

ADVERTISEMENT

If the FBI didn't brief the campaign, Grassley wants to know why not and who was involved in the discussions and if a controversial opposition research dossier — which has been a frequent target of Grassley's — impacted the decision.

Grassley is asking that the FBI respond to his letter by Oct. 4.

CNN reported this week that the FBI wiretapped the phones of Paul Manafort, Trump's former campaign chairman, during and after the 2016 campaign, using a secret court order obtained under the Foreign Intelligence Surveillance Act (FISA).

Manafort has emerged as a key figure in special counsel Robert Mueller's investigation into Russia's election meddling and potential ties between Moscow and Trump campaign officials.

Pointing to the CNN report, Grassley notes in his letter that recent press reports indicate that Manafort was being investigated by the federal government.

"This raises the question of whether the FBI ever alerted Mr. Trump to the FBI’s counter-intelligence concerns regarding his campaign manager and others associated with the campaign," he wrote.

Former FBI Director James Comey told the Senate Intelligence Committee in June that "there are a variety of defensive briefings given to the incoming Administration about the counterintelligence risk."

But Grassley notes his answer was "unclear" about if the briefings were tied to concerns the bureau had about a Trump campaign official.

Grassley, as chairman of the Judiciary Committee, has launched broad probes into Russia's election meddling, potential political interference into FBI investigations and Comey's firing.

Grassley had initially issued a subpoena against Manafort to force him to testify, but then dropped it. He told reporters this week that whether or not he issued another subpoena could depend on the outcome of Mueller's investigation.